The present invention relates to a hydraulic lost motion apparatus for an engine valve train that achieves lashless valve operation as well as two sets of valve motion in response to signals from an engine controller in an on/off manner. Without limitation, the present invention is useful in the operation of an internal combustion engine and particularly, for example, in the operation of an exhaust valve train in a power mode and a compression brake mode.
There are instances where it is desirable to provide lashless valve operation for an internal combustion engine wherein mechanical adjustment for valve train assembly tolerance, thermal growth, wear is not necessary. Furthermore, it would be desirable to provide a valve actuation system for an internal combustion engine that combines the functions supplied by the conventional hydraulic overhead housing compression brake and the conventional mechanically lashed rocker arm assembly. Such an achievement would reduce manufacturing costs and eliminate lashing operations during manufacture and servicing of such an internal combustion engine. The means to achieve this improvement could also be applied to other engine functions such as internal EGR control, peak cylinder pressure control, airflow optimization by shifting between a low lift and a high lift profile, or even cylinder deactivation. An exhaust valve train is known wherein an integrated exhaust rocker arm assembly that includes a rocker arm having a piston and control valve, which is hydraulically controlled by a remotely mounted solenoid valve to effect a braking mode. For example, U.S. Pat. No. 5,626,116 to Reedy et al. that was granted on May 6, 1997 relates to a dedicated compression braking system for a internal combustion engine wherein an exhaust valve opens (a) near the end of an expansion stroke in a power mode of operation and (b) in a variable timed relationship to the compression stroke in brake mode. The braking system includes first and second exhaust valve actuating means for causing the exhaust valve to reciprocate in the power mode and braking mode, respectively. The first exhaust valve actuating means includes a power mode rocker lever pivotally mounted adjacent the exhaust valve for opening the exhaust valve in the power mode. A first cam means is provided to pivot the power mode rocker lever. The second exhaust valve actuating means includes a braking mode rocker lever pivotally mounted adjacent the exhaust valve for opening the exhaust valve in a braking mode. A second cam means is provided to pivot the braking mode rocker lever. The braking system of the Reedy et al. patent requires, the use of two rocker levers, one for the power mode and one for the braking mode. In addition, the apparatus described in Reedy et al. does not provide for lashless operation.
It is an object of the present invention to provide an improved engine valve train.
A further object of the present invention is to provide an engine valve train that effects lashless valve operation.
It is another object of the present invention to provide an engine exhaust valve train that eliminates the conventional overhead housing compression brake and thus achieve a lighter, more compact engine valve train.
Another object of the present invention is to provide an engine exhaust train that is less costly to manufacture and service.
It is also an object of the present invention to selectively achieve two sets of valve motion for either exhaust or intake valve train for desirable engine management objectives.
It is a further object of the present invention to deactivate the valve events, again for desirable engine management objectives.